In response to consumer demands, portable electronic devices, such as calculators and selective call receivers, are becoming more compact and multi-functional in order to meet a variety of users' needs. The additional functionality may require additional components. Yet, as the size of portable electronic devices decreases, the surface area of the device decreases, limiting the space available for externally mounted components. In addition, the smaller devices have less internal volume, further limiting the devices' components. Moreover, the electronic devices must derive their power solely from an energy source contained within or externally attached to the electronic devices.
Typically, information can be communicated to an electronic device via a radio frequency (RF) link, an externally mounted data port connection such as an RS232 data port, or a group of contacts externally mounted on the device.
The RF link, though, is a time consuming way to download test data and device reprogramming information, and RF air time is limited. Moreover, the RF link requires additional components for demodulation prior to decoding the signal communicated.
Special groups of contacts or data communications ports can provide a direct coupling to a decoder within the electronic device. Regrettably, the ports and contacts have many additional components associated with them as well as intrinsically safe (UL listing) requirements. Since portable electronic devices are primarily carried by the users, externally exposed metal contacts may become corroded resulting in a high resistance and unreliable communication. Moreover, the ports or contacts require careful handling in coupling to prevent damage to the electronic device's components from a difference in static potential between the electronic device and the coupled device.
More recently, a serial light interface comprising an optical coupler on each device provides intercommunication and improves static immunity. Conventionally, an optical coupler comprises an externally mounted light emitting apparatus for transmitting information and an externally mounted photodetection apparatus for receiving information such as that disclosed in U.S. Pat. No. 4,348,744. Regrettably, the optical coupler of existing electronic devices requires additional components and consumes additional power.
Thus, what is needed is a reliable communications interface which requires few or no additional components, has little or no additional power consumption and has increased static immunity.